1. Field of the Invention
The present invention relates to an X-ray diagnosis apparatus and a method thereof and, more particularly, to an X-ray diagnosis apparatus which examines by X-ray photography or fluoroscopy a plurality of regions of a subject under examination consecutively and a method thereof.
2. Description of the Related Art
One method of diagnosing diseases in circulatory organs is catheter examination. This catheter examination is made in an examination room in which an X-ray diagnosis apparatus and a bed for catheter examination (hereinafter referred to as a "catheter bed") are installed.
FIG. 1 is a schematic representation of the whole structure of a prior art X-ray diagnosis apparatus.
Under the control of an X-ray controller (not shown) an X-ray tube 1 irradiates x-rays onto a subject 2. The X-rays transmitted through the subject 2 are converted by an image intensifier 3 into an optical image, which, in turn, is entered through an optical system (not shown) into a TV camera (not shown) for conversion into a TV picture signal. The subject 2 is laid on a top board 5 placed on a catheter bed 4. The top board 5 is movable in both A and A' directions as shown in FIG. 1.
Using such an X-ray diagnosis apparatus as described above, a catheter examination of blood vessels in a leg is made as follows.
A catheter is inserted into a blood vessel and a blood vessel contrast medium is injected from the tip of the catheter into the blood vessel. The top board 5 of the catheter bed 4 on which the subject 2 is laid is moved in steps in the direction of A in FIG. 1 in synchronism with the speed with which the contrast medium progresses from the abdomen to the foot (hereinafter this movement is referred to as "leg stepping"). While the top board 5 is moved, examination by X-ray photography or fluoroscopy is made on the subject 2, using the X-ray tube 1 at regularly spaced intervals, i.e., for each of predetermined positions (or desired positions) of the leg of the subject (hereinafter referred to as "stage position"). This operation is hereinafter referred to as simply "stepping photography". This stepping photography permits visual observation of blood vessels in the entire leg, permitting an understanding of the conditions of diseases in circulatory organs of the subject.
With the leg stepping described above, it is required that a stenosis of a blood vessel of the subject 2 be located in the center of an X-ray image. That is, it is required to position the subject 2 by means of fluoroscopy prior to X-ray examination so that a desired portion of the subject 2 is placed in position, i.e., in the predetermined stage position. In almost every case, the stenosis will be produced at the place below the knee where three blood vessels branch off. The positioning is normally performed so that the place where blood vessels branch off is set in the fourth stage position. For the catheter bed 4 that is currently used, the number of movement steps is fixed at four and the number of stage positions is fixed at five. It is therefore difficult to position the subject 2 so as to entirely cover from an abdomen to an end of foot (hereinafter referred to as a "foot end"). If the foot tip cannot be covered, a method of photographing only the foot separately is adopted.
The leg stepping as described above will be described in more detail with reference to FIG. 2.
FIG. 2 is a diagram for use in explanation of the stepping photography of leg stepping. In the conventional leg stepping, the stepping photography is sequentially performed at successive stages from the first stage (the stepping starting position) to the fifth stage, these stages being regularly spaced at a fixed interval (hereinafter referred to as "step size"). As described above, not only the step size but also the number of stages is fixed. If, therefore, in FIG. 2, the stepping photography is started at the first stage, the portion below the knee of the subject 2 will not necessarily be placed in the center of the photography area at the fourth stage because each subject to be examined has a different height. Since the leg length also varies from subject to subject, the entire leg will not necessarily fit within the scope of the stepping photography.
On the conventional catheter bed for leg stepping, the number of steps and the step size are fixed as described above. Therefore, in order to cover the desired photography scope fully, the stepping photography start position (e.g., the abdomen of a subject) is shifted backward and forward for position adjustment. In this case, in order to position a stenosed portion to be photographed, i.e., the place where three blood vessels branch off, in the fourth stage suitably, it is required to shift the top board 5 over and over again with X-ray fluoroscopy carried out for verification. For this reason, the subject 2 and an operator will be exposed to more X-rays than is necessary. Further, since the scope of stepping photography varies with the height of each subject to be examined, the positioning work is difficult and takes a lot of time.
In the above description, problems with leg stepping are described with respect to the case where the catheter bed 4 is shifted. The same can be said of the case where the X-ray tube is shifted for the stepping photography.
In the conventional X-ray diagnosis apparatus, as described above, since the number of steps and the step size for stepping photography are fixed, the positioning of a subject under examination has to be performed by shifting the top board 5 utilizing fluoroscopy for verification thereby to change the stepping photography start position so that the desired photography scope can be covered and a body portion to be examined can be placed in position. With this method, however, the positioning work is difficult because the scope of photography varies with the height of each subject to be examined.